DC Superconducting Fault Current Limiter Research Articles

Parametric design method and application study of a 160‐kV resistive‐type DCSFCL in a three‐terminal flexible DC transmission system

AbstractThe intermittent access of renewable energy sources leads to a significant increase in fault short‐circuit currents in power grid. DC superconducting fault current limiters (SFCL) can limit short‐circuit currents in flexible DC transmission systems, which work in combination with direct current circuit breaker (DCCBs) to protect the grid system effectively. However, for the parameter design of DC superconducting fault current limiter (DCSFCL), it is difficult to balance the economics of the device and its adaptability to different fault situations. In this paper, a cross‐mapping design methodology for the DCSFCL is proposed and applied in the Nan'ao flexible DC transmission project, China. A cross‐mapping method is designed combining the critical parameters of DCSFCL and the system parameters. A three‐terminal simulation model of the flexible DC transmission system is constructed through MATLAB/Simulink and the design process of DCSFCL parameters is introduced. A cyclic calculation approach is proposed for the design of DCSFCL parameters through three fault conditions of the power system. Meanwhile, impact current short‐circuits test and artificial ground short‐circuit test were conducted on the prototype. Test results show that the designed DCSFCL meets the requirements of practical applications.

Surface Dielectric Characteristics of GFRP and PTFE in Cryogenic Environment Under the Switching Impulse Superimposed on DC Voltage

For insulation materials utilized in DC superconducting fault current limiter, surface discharge along the interface is more damaging to the insulation relative to penetration breakdown. Therefore, for the reliable and economical insulation design of DC superconducting fault current limiter, it is very important to investigate an insulation materials and study the surface dielectric characteristics. Additionally, DC superimposed switching impulse can cause critical stress to the insulation of DC superconducting fault current limiter and can potentially result in breakdown. Therefore, the insulation materials of DC superconducting fault current limiter must have sufficient surface distance to prevent surface discharge under DC superimposed switching impulse. In this paper, the surface breakdown tests were performed by applying DC superimposed switching impulse to glass fiber reinforced polymer (GFRP) and polytetrafluoroethylene (PTFE) specimen in cryogenic environment. Surface dielectric characteristics according to positive and negative polarities of DC and switching impulse were analyzed. In addition, the surface dielectric characteristics were analyzed by selecting the gap distance. From the experimental results, the surface dielectric strength of GFRP was higher than that of PTFE, but the difference in surface dielectric strength between GFRP and PTFE decreased as the gap distance increased. The surface breakdown voltage of PTFE was lowest at the superposition of positive DC and positive switching impulse. However, GFRP has the lowest surface breakdown voltage when negative DC superimposed positive switching impulse. Consequently, it is possible to design the optimal surface distance of solid insulation materials in DC superconducting current limiter by considering the superposition of DC and switching impulse polarity.

Study on the influencing factors to reduce the recovery time of superconducting tapes and coils for the DC superconducting fault current limiter applications

Superconducting fault current limiters (SFCLs) are important in improving the stability of electrical power systems. However, the existing resistive-type DC SFCL has a long recovery time, which cannot meet the requirements of power system auto-reclosure. Thus, it is necessary to investigate the methods of reducing recovery time of SFCLs. In the simulations on superconducting tapes, there is a lack of investigation about the effects of design factors of superconducting tapes and coils such as material, thickness, coil radius, coil winding method on recovery characteristics. The objective of this study is to obtain the effects of material and geometric properties of superconducting tapes and coils on recovery characteristics and obtain methods to reduce the recovery time. The recovery times under different conducting currents are also compared by simulations and experiments to verify simulation accuracy. The maximum error is below 40% and most of the cases have an error below 10%. Besides, by increasing tape thickness, the recovery time can be reduced by 22%. Tape materials and coil winding methods can be designed according to the auto-reclosure and current-limiting requirements of the power systems. The research provided directions for the design of superconducting tape and superconducting coil for resistive-type DC SFCLs.

Further study of a novel inductive SFCL for multiterminal HVDC systems

Multiterminal high voltage direct current (HVDC) systems are developing rapidly lately. However, the high rising rate of fault current and the lack of interrupting capacity of the available DC circuit breakers hinder the further development of multiterminal HVDC systems. Being aimed at the challenge, this paper proposes a novel inductive DC superconducting fault current limiter (SFCL) to cooperate with available DC circuit breakers to cope with the short-circuit fault current in a multiterminal HVDC system effectively. In the normal power transmission of a multiterminal HVDC system, the SFCL presents low impedance and enables a smooth reclosing operation after an interruption. It is able to make a maximum use of the permeability of the iron core to offer a large inductance to curb the rising rate of the fault current in the early few milliseconds as a fault takes place. In addition, it can have an adjustable current limiting threshold to match the different requirements of different grid protection schemes. In this paper, first the working principle of the proposed SFCL is introduced. Then the experimental results on a concept-proofing prototype are reported and analyzed. The experimental results have verified the principle and functional ability of the proposed SFCL.

Research on DC overcurrent characteristics and life prediction of YBCO tapes

The repeatability of superconducting DC limiters has not been introduced by other literature. Understanding the performance degradation characteristics of high-temperature superconducting (HTS) tapes under the overcurrent is of great significance for popularizing the application of a resistive-type DC superconducting fault current limiter. In this paper, the threshold experiment and repeated DC overcurrent experiment of HTS tape were carried out. With the critical current decay of the tapes under repeated DC overcurrent recorded, the current threshold under the DC overcurrent was obtained. And the performance degradation characteristics of the tapes under different repeated overcurrents were analysed, the resistance characteristics of the samples during different currents were compared. The results show that the DC overcurrent threshold of the copper-encapsulated second-generation (2G) YBCO tapes samples of Suzhou Advanced Materials Research Institute is 2.3/4 ms/3700 A. Under the repeated overcurrent, the performance degradation of the samples is abrupt, and the critical value is between 2.3/4 ms/3500 A and 2.3/4 ms/3550 A. The overcurrent has a limited influence on the magnitude of the resistance and will not affect the change trend of the resistance. The resistance at the falling edge of the current was greater than that at the rising edge of the current. The simulation was carried out by using COMSOL Multiphysics, and the simulation results matched the experimental results. The life prediction model of the samples was established and it was found that there is a custom equation relationship between the reliability of superconducting tapes and the number of the overcurrent, and the performance decline of this kind of samples is catastrophic.

Optimized design and electromagnetic analysis of a hybrid type DC SFCL in MMC system

With the increase of DC transmission voltage and capacity, large dc fault current becomes an important issue due to the bottleneck of the capacity of the DC breaker. In order to solve the problem, we have proposed a novel hybrid type DC superconducting fault current limiter (DC SFCL) in our previous papers. Based on a series of previous researches, some improvements are made to design the hybrid type DC SFCL for application in a MMC system in this paper. The target is to limit short circuit current and avoid converter valves blocked when the DC short circuit occurs. In consideration of cost and stability, combined with the transient characteristics and parameter matching of the DC SFCL, an effective optimization design method consisting of electromagnetic theory and intelligent algorithm is proposed, which can obviously promote the utilization efficiency and stability of YBCO coated conductors. According to the optimization design method, a design scheme of the DC SFCL is put forward. Combined with three operation states of the DC SFCL (normal state, current limiting state I and current limiting state II), a corresponding finite element model is established to simulate and evaluate the performance of superconducting coil in the DC SFCL, which further reveal the AC loss characteristics of superconducting coil during current limiting process.

Quench recovery time of an optical fiber encapsulated resistance-type DC superconducting fault current limiter coil determined by a Raman-based distributed temperature sensing system

The superconducting fault current limiter (SFCL), as a very important power facility for high voltage DC system, can consume fault current energy and make DC breakers cut off fault transmission lines successfully. For the moment of reclosing DC breakers, the quench recovery time of the SFCL must be determined in advance. In this article, according to the design requirement of a 160 kV/1 kA resistance type DC SFCL in the Nan’ao multi-terminal flexible HVDC transmission demonstration project, the quench recovery time of a SCFL coil wound by two optical fiber encapsulated high temperature superconducting (OFE-HTS) tapes was checked by our optimized Raman-based distributed temperature sensing (Rm-DTS) system. The experimental results show that the used OFE-HTS tapes can withstand a 1500 A/100 ms AC short circuit current impact and are qualified with the SFCL. Furthermore, the quench recovery time of the SFCL coil measured by the Rm-DTS was 2930 ms. During the quench, the highest temperature zone occurred near the center of the SFCL coil.

Design and Tests of a 160-kV/1-kA DC Superconducting Fault Current Limiter

DC Superconducting fault current limiter (SFCL) can be used to reduce the fault current of voltage source converter-based high-voltage direct current (VSC-HVdc) transmission systems, thereby significantly reducing the manufacturing difficulty and cost of dc circuit breakers. The authors aim to develop a 160-kV/1-kA resistive type dc SFCL, and apply it in the VSC-HVdc transmission system in Nan'ao of China. In order to verify the feasibility of the transmission voltage dc SFCL, the research is divided into two stages, and the results of the first stage are presented. The rated voltage and current of the developed dc SFCL is 160 kV and 1 kA, respectively, and the current limiting resistance is no less than 2 Ω within 10 ms, which is 1/4 of the second stage prototype. The used superconducting material is stainless steel reinforced yttrium barium copper oxide (YBCO) conductor produced by Shanghai Superconductor. A three terminal structure is presented to meet the different operation parameters. A 160-kV dc SFCL prototype has been fabricated, and the prototype has passed the steady-state current test of 1 kA, the dc withstand voltage test of 252 kV within 1 min, the lightning impulse test of 550 kV/1.2 μs/50 μs, and the operating impulse test of 450 kV/250 μs/2500 μs. The average operating thermal loss of the device at rated current is 652 W. Power switching test results show that the developed SFCL could generate the desired limiting resistance of about 2.2 Ω in less than 10 ms, and the maximum fault current duration time could be as high as 60 ms.

Design and performance tests of a 160 kV/1.0 kA DC superconducting fault current limiter

Superconducting fault current limiter (SFCL), which is used in voltage source converter based high voltage direct current (VSC-HVDC) transmission systems to limit fault currents and protect the grid together with DC circuit breakers, could improve system safety and stability. The first transmission voltage DC SFCL is developed in China, and it has been applied in the 160 kV VSC-HVDC transmission system in Nan’ao. The electromagnetic design as well as insulation analysis of the current limiting unit is presented, where the current limiting unit is composed of 96 bifilar coils made of stainless steel reinforced YBCO tapes. The liquid nitrogen at the temperature of 77 K is used as the cooling and insulation medium, and the liquid nitrogen is cooled by a closed-loop cryogenic system consists of 3 G-M refrigerators. The 160 kV DC SFCL prototype has been fabricated, and the prototype has passed the steady-state current test of 1 kA, the DC withstand voltage test of 252 kV within 1 min, the lightning impulse test of 550 kV/1.2 µs/50 µs and the operating impulse test of 450 kV/250 µs/2500 µs. Power switching test results show that the developed SFCL could generate the desired limiting resistance, and the maximum fault current duration time could be as high as 60 ms. The developed prototype has been installed in the Nan’ao VSC-HVDC transmission system, and put into operation on August 17, 2020.

Experimental Tests of DC SFCL Under Low Impedance and High Impedance Fault Conditions

DC system protection is more challenging than that for AC system due to the rapid rate of rise of the fault current and absence of natural current zero-crossing in DC systems. Superconducting fault current limiter (SFCL) in DC systems is a promising technology to reduce the fault current level and the rate of rise of the fault current, and also SFCLs have no resistance during normal operation. In this paper, the behaviors of an SFCL coil are investigated under both low impedance and high impedance fault conditions in DC systems. In the low impedance fault condition system, the SFCL coil performs effective limitation of the fault current level under different prospective fault current levels. The application of SFCLs with limited inductance in the DC system can be a potential solution to effectively suppress the fault current under low impedance short-circuit faults. The SFCL coil under the high impedance fault condition can only limit the prospective fault current when it is much higher than the critical current of the coil.

Current limiting tests of a prototype 160 kV/1 kA resistive DC superconducting fault current limiter

High voltage direct current (HVDC) transmission technology has begun to play a great role in power transmission industry over the last decade. However, short-circuit fault seriously threatens the safety of an HVDC network. In order to reduce the fault current level of an HVDC network, utilizing a superconducting fault current limiter (SFCL) was proposed by researchers and engineers worldwide. Recently, Guangdong Grid Company of China Southern Power Grid, Co. has led a project to develop a 160 kV/1 kA resistive type DC SFCL. As a middle-step objective, a 160 kV/1 kA laboratory prototype has been developed. Due to a facility with an adequate capacity for testing such DC equipment is practically inaccessible, the current limiting performance of the prototype cannot be tested with a straightforward current limiting experiment. In practice, effectual alternative methods have to be adopted. Since the AC half-wave impact method requires less equipment and cost than the DC impact method, we took on an AC half wave impact current method to evaluate the current limiting function of the prototype alternatively. In this paper, we report the procedures and results of these tests.

Analysis of the DC Fault Current Limiting Characteristics of a DC Superconducting Fault Current Limiter Using a Transformer

Recently, a lot of interesting research has been conducted to solve the fault current problem of the DC system. In long-distance transmission, DC transmission is more economical than AC transmission. The connection of power grids with a DC system can also better control the power flow and provide high stability. However, the control of the fault current in a DC system is more difficult to handle than in an AC system because the DC system does not make a zero point, unlike the AC system. In addition, there is a disadvantage, in that an arc occurs when a circuit breaker operates. In this paper, a new type of DC superconducting fault current limiter (SFCL) is proposed. This new type of SFCL is composed of two superconducting elements, a current limiting resistor/reactor (CLR), and a transformer. With the proposed SFCL, the DC fault current limiting experiments were performed and the DC fault current limiting characteristics of this SFCL due to the component of the CLR were analyzed.

Design and Test of 40-kV/2-kA DC Superconducting Fault Current Limiter

In this article, a general scheme of a 40-kV/2-kA resistive type dc superconducting fault current limiter (SFCL) is suggested, which could be utilized to suppress the surge current caused by short-circuit faults in voltage-source-converter HVdc (VSC-HVdc) power grids. This dc SFCL is designed and fabricated with 6 coil modules in parallel and 4 in series. In order to investigate the current-limiting performance of the dc SFCL under the rapidly rising fault current, the SFCL is tested on the platform with a pulsed dc impact generator. Besides the property of current limitation, the current capacity, insulation and quench recovery performance of such SFCL are also tested. Results indicate that the critical current of SFCL is larger than 2050 A at 69 K, and the dc withstand voltage is larger than 74 kV in 2 h. During the 9-kV dc impact test, the short-circuit current could be limited to 8842 A, and the quench recovery time is less than 200 ms.

Design and Performance Test of a 20-kV DC Superconducting Fault Current Limiter

A resistive-type dc superconducting fault current limiter (SFCL) is developed for the fault current limiting at the Suzhou Nami substation. The rated voltage and current are 20 kV and 400 A, respectively. The prospective peak value of the short-circuit current is about 3.5 kA, and the current could be limited to less than 2.1 kA by the SFCL. The SFCL uses about 1800-m stainless steel reinforced yttrium barium copper oxide (YBCO) conductor. According to the testing results, the developed SFCL has passed the dc withstand voltage test at 50 kV/min, the full-wave lightning impulse voltage at 95 kV, and the dc power switching test with a peak value of 2.26 kA and a fault duration of 16.5 ms.

Parameter Matching and Optimization of a Hybrid Type DC SFCL Considering the Transient Characteristics of VSC-Based DC Systems

Voltage source converter-based (VSC-based) DC systems play an important role in connecting large-scale renewable energy and distributed energy, but they are vulnerable to DC short-circuit fault and lacks mature protection devices and appropriate protection strategies. Therefore, a hybrid type DC superconducting fault current limiter (H-SFCL) is proposed and the current limiting mechanism of the SFCL is analyzed. According to the requirements and strategies for protection, several different effective parameter matching and optimization methods of the H-SFCL are proposed by combining optimization algorithms and two short-circuit transient calculation models of VSC-based DC systems. The optimization methods proposed in this paper are compared and analyzed in terms of convergence, running time, calculation range and stability of optimization results, revealing their respective calculation characteristics. Finally, the effectiveness of parameter matching and optimization methods are well validated by comparison and analysis of simulation. The proposed methods can select a good parameter matching scheme of the H-SFCL to deal with different requirements.

Quench and Recovery Characteristics of Solenoid and Pancake SFCLs Under DC Impact Current

With the rapid development of the voltage source converter-based high voltage direct current (VSC-HVdc) power systems, as one of the methods for the suppression and interruption of short circuit current, resistive type dc superconducting fault current limiter (SFCL) is getting more and more attention. As SFCL will quench during the current limiting process, it is necessary to complete the quench and recovery process before the automatic reclosing of VSC-HVdc power systems. In this article, simulation and experimental analysis on SFCL are carried out. The superconducting tape used in the SFCL is the AMSC 8602 YBCO superconducting tape. It is concluded that the simulation results obtained by thermal conduction model using lumped parameter method are basically consistent with experimental results. With the increase of dc impact current and dc impact duration, recovery time of SFCL increases. Recovery time of the solenoid SFCL and the pancake SFCL under different placement modes differs, which is related to the heat dissipation space and the accumulation of bubbles.

A New Type of DC Superconducting Fault Current Limiter

A new type of Superconducting Fault Current Limiter (SFCL) for dc applications is proposed. This SFCL consists of a current transmission/limiting coil, an iron-core, and a set of superconductor rings. The superconductor rings are placed between the current transmission/limiting coil and the iron-core. For application, the current transmission/limiting coil is connected in series to a dc transmission line. During normal power transmission, magnetic flux coupling between the current transmission/limiting coil and the iron-core is prevented by the magnetic shielding of the superconductor rings, and the current transmission coil has low impedance. Because of shielding effect of the superconductor rings iron-core has high permeability at the beginning of short circuit, current-limiting coil can effectively limit fault current rise. When the fault current reaches a certain level, the superconductor rings will quench and the shielding effect is greatly reduced. The current-limiting coil strengthens the coupling with the iron core, increases the inductance, and will suppress the further increase of the fault current. A laboratory proof-of-concept prototype was made to demonstrate the feasibility of the idea. Experiments have been carried out with the prototype. In this paper, we will introduce the detailed information of the principle, the prototype, and the experimental results. In addition, a design of the new type of dc SFCL is installed in a ±160 kV high-voltage direct current system.

Influencing Factors on Quench and Recovery of YBCO Tapes for DC Superconducting Fault Current Limiter

Quench and recovery characteristics are the most important characteristics of dc resistive type superconducting fault current limiters (SFCLs). In the normal state, the superconducting tapes of SFCLs stay in superconducting state without power loss. However, if there is a thermal disturbance energy impact to the superconducting tapes, the tapes may be quenched, and sometimes even break once their temperature is too high. After the thermal disturbance, the tapes may recover to superconducting state again. A numerical analysis method was proposed to analyze quench propagation and recovery characteristics of the YBa 2 Cu 3 O 7-δ tapes based on thermal conduction theory. The objective of this paper is to obtain the influencing factors such as magnitude of thermal disturbance, transport current, material of the stabilized layer and cooling on quench, and recovery properties of dc resistive type SFCL. Numerical analysis results show that the temperature and voltage of the tape increased while the transport current through the tape and the magnitude of thermal disturbance increased. The quench propagation velocity was higher and the recovery time was shorter for copper stabilized layers than stainless steel stabilized layers.

Tests and Analysis of a Small-Scale Hybrid-Type DC SFCL Prototype

In recent years, high-voltage dc power transmission is widely developed in the world. However, it is difficult for the existing dc breaker to cut off the fault transmission line with large short-circuit fault current. In a short-circuit fault of dc systems, short-circuit fault current is composed of initial transient impulse current and steady-state fault current. Therefore, a hybrid-type dc superconducting fault current limiter (SFCL) is proposed with two-stage current limiting capability. In the early stage of short-circuit fault, initial transient impulse current is limited by inductance and resistance. In the later stage of short-circuit fault, a sustained and steady current-limiting resistance is provided by the dc SFCL. A small-scale prototype of the dc SFCL is developed and the parameter design of the dc SFCL prototype is presented. According to the experimental tests and simulation analysis, the design scheme's effectiveness can be confirmed from high current-limiting ratio. Based on experimental tests and simulation analysis, the current-limiting characteristics and energy loss characteristics of the hybrid-type dc SFCL have been well verified.

Magnetic Field and Characteristic Analysis of the Superconducting Fault Current Limiter for DC Applications

The dc superconducting fault current limiter is an important component of HVdc power supply protection systems. The critical current value of the superconducting tape is associated with the magnetic field around it and the electromagnetic force received by the superconducting coil in case of a power supply system faults may damage it. Thus, it is crucial to consider the magnetic field distribution and the electromagnetic force when doing the performance analysis and the optimization design of superconducting fault current limiters. In the paper, the static and the transient magnetic field FEM computational models of dc superconducting fault current limiters are built for both the normal operation status and in case of a the short-circuit fault. Using the static magnetic field model, the magnetic field distribution of a disk and a cylinder superconducting coils is calculated. The transient magnetic field distribution and the electromagnetic force for the two coils are analyzed using the transient magnetic field model.